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Risk Assessment For Exotic Spiders

12 June 2002

Public Views Sought On Risk Assessment For Exotic Spiders Associated With Imported Table Grapes

Public views are being sought on proposed strengthened measures to reduce the risk of exotic spiders hitchhiking to New Zealand in bunches of table grapes from California.

A detailed assessment of the biosecurity risk to New Zealand posed by exotic spiders entering on imported table grapes has been completed and its associated documents were released for public submission today, with submissions required by 24 July 2002.

Trade in table grapes from California was suspended in November 2001 following the post-border detection of four live black widow spiders and a number of other exotic spiders over a three month period.

A special biosecurity project team was convened to produce the assessment, consisting of officials from the Ministry of Agriculture and Forestry (MAF), Department of Conservation (DOC) and Ministry of Health (MoH). The process was led by MAF’s Indigenous Flora and Fauna team.

Project spokesperson Christine Reed of MAF, said the risk assessment consists of three separate documents covering: environmental risk of entry and establishment of exotic spider species including black widow spiders; potential health impacts and, recommended measures to reduce the risk to achieve an acceptable level of protection.

"The inter-agency approach we have followed has allowed us to bring a broad level of technical expertise to what is a complex biosecurity issue, to ensure a result that sets a robust and rigorous baseline for us to operate from in the future," said Ms Reed.

"Put simply we began from the basis that any trade involves accepting some risk and achieving zero risk isn't realistically practical. The agencies then worked towards deciding likely levels of risk for a variety of situations. Because we are assessing the risk from the different perspectives (to the environment and to human health), we then need to weigh up all available information to ensure the assessment is fair and balanced.

“While the project team have thoroughly examined the potential options for risk mitigation at a level appropriate for the level of risk there will be quite possibly still low numbers of post border detections of exotic spiders associated with table grapes. Post-border risk reduction measures have been recommended however to further reduce the public health risk of these spiders.

“It is also part of our role to raise awareness and understanding of biosecurity issues and to increase our level of preparation for the contingency that new species, including exotic spiders, will be found in New Zealand from time to time.

“This assessment illustrates that biosecurity risks are not limited to the potential impact of pests and diseases on our primary sector industries - they include risks to public health and to New Zealand’s unique indigenous flora and fauna.” she said

For further information contact:

Christine Reed, MAF Biosecurity Coordination Group

(04) 470 2576 or by email to


Philippa White, Communications Adviser, MAF Biosecurity

(04) 498 9948 or 025 223 1875

Internet links to the three risk assessment documents are located at: under Forums

See also attached "Overview of Assessment Documents For Exotic Spiders Associated With Imported Table Grapes".

Invitation for Submissions

on the Assessment of Risks of Exotic Spiders

Associated with Imported Table Grapes

The Import Health Standard for table grapes from the United States of America (State of California) was suspended in November 2001. Trade will remain suspended until the Import Health Standard is reissued. This action followed the post-border detection of four live black widow spiders and a number of other exotic spiders over a three month period. Concerns were raised by the Ministry of Health and the Department of Conservation that the level of protection (from risks to human health and the environment) was no longer acceptable through this pathway.

An inter-agency project team (MAF Biosecurity, Department of Conservation and the Ministry of Health) was established in late November to oversee development of risk assessments addressing the concerns over this pathway. A Health Impact Assessment discussion document has been prepared by the Ministry of Health, and a Pest Risk Assessment by the Indigenous Flora and Fauna team of MAF Biosecurity Authority. The Indigenous Flora and Fauna team has also drafted recommendations for mitigation measures to inform the process of deciding on a revised Import Health Standard.

The three documents available with this cover note have been peer reviewed within and between the project team agencies. The Ministry of Agriculture and Forestry, Department of Conservation and Ministry of Health support the two technical assessments and the recommendations for mitigation measures.

These three documents are now available for public review and submission. The documents, or links to the documents, are available from either of:

MAF website at

Ministry of Health website at under Forums

Comments on all three documents should be provided in writing before 24 July 2002 to:

Ministry of Agriculture and Forestry

Indigenous Flora and Fauna Team

MAF Biosecurity Coordination

Ministry of Agriculture and Forestry

PO Box 2526


Following a review of submissions and incorporation of relevant comments into the documents, it is proposed that these documents will form the basis for a revised Import Health Standard.

The Project leader is Christine Reed, National Adviser, Indigenous Flora and Fauna, MAF. Christine can be contacted by email to or by fax to (04) 470 2751

Document 1:

MAF Biosecurity Pest Risk Assessment: Spiders Associated with Table Grapes from United States of America (State of California), Australia, Mexico and Chile

The Pest Risk Assessment (PRA) concentrated on seven species of spider, all from California. The species were:

Latrodectus mactans (black widow spider)

Latrodectus hesperus (Western black widow spider)

Latrodectus geometricus (brown widow spider)

Cheiracanthium inclusum (yellow sac spider)

Phidippus johnsoni (Johnson spider or redback jumping spider)

Gea heptagon (orb-web spider)

Oradrassus assimilis

For the purposes of the risk assessment four factors are given as affecting the likelihood of spiders entering New Zealand in any life cycle stage. Those factors are:

- the area from which the commodity is sourced

- an association with the commodity itself (i.e. the grape bunches)

- the volume of the commodity imported

- the quarantine measures applied.

A further six factors are identified as affecting survival and establishment. Those are:

- suitability of climate at time of entry, including humidity

- availability of habitat close to entry sites

- the number of founder individuals

- natural mortality after entry

- handling of the grape bunches after entry

- presence of any natural enemies and competition from other spiders.

It is noted that the spiders being assessed generally require periods of sustained warm conditions to reach maturity. However they can survive for months at a time on no food and at low temperatures and generally have high survival rates.

Phidippus johnsoni while not considered a significant human health risk is assessed to be a low to moderate risk to the environment - balancing a low risk of entry and moderate risk of establishment with a high potential consequence to the environment. This is related to the likelihood of establishing in habitats that overlap with and impact on native spiders and possibly other invertebrates (e.g. endemic moths and beetles). Based primarily on the low risk of entry, while also allowing for likely habitats, the overall risk to the environment from the six other species is low.

Document 2:

Towards a Health Impact Assessment Relating to Venomous Spiders Entering New Zealand in Association with Imported Table Grapes : A Discussion Document

The Ministry of Health's document found that black widow spiders (the spiders that have been detected post-border on bunches of grapes and that have the potential to cause harm to people) are a moderate health hazard. Black widow spider bites in some cases require medical intervention, and in a small number of cases the effects of bites can be severe. But not all bite victims suffer symptoms beyond the initial bite and victims that do suffer further symptoms usually recover in three to five days.

The Ministry of Health assessment also found that post-border detections of black widow spiders provide for high individual exposure, creating a moderately high public health risk and that the public health risk posed by the scenario of black widow spiders becoming established in New Zealand is moderately low, due to the risk of black widow spiders establishing in New Zealand being low.

The Ministry of Health has recommended a number of post-border risk mitigation options that would, when implemented, enable members of the public finding spiders to take appropriate actions and provide for more effective public health responses to spider bites (by those spider species of concern). The document presents cost-effective approaches for risk management related to anti-venom stores, professional training and public health awareness.

It is acknowledged that there have been no reported bites from exotic spiders detected as a result of the importation of grapes despite the moderately high level of individual risk when exposed.

NOTE: Both the Pest Risk Assessment and the Health Impact Assessment consultation documents are qualitative assessments and both draw attention to gaps in definitive information about a number of important factors.

Document 3:

Mitigation Measures for the Management of the Risks Posed by Exotic Spiders Entering New Zealand in Association with Imported Table Grapes

A range of alternative or additional measures that will have a mitigating effect on the risks posed by exotic spiders have been identified. Some of these measures may in fact serve a dual role and mitigate both the phytosanitary and exotic spider (health and conservation) risks. Some 10 different mitigation options are presented for consideration as well as an assessment of the potential efficacy of fumigation, pesticide applications, irradiation, temperature manipulation and increased inspection rates.

Overall no changes to the current risk mitigation measures are proposed for imports of table grapes from Australia, Chile or Mexico. Formalisation of the contingencies for detections of exotic spiders in New Zealand originating from these countries will be required to ensure consistency with the contingencies for table grapes from the USA.

For imports of table grapes from the USA (State of California) there are some 10 recommended mitigation measures and a set of proposed contingencies.

Several of the recommended mitigation measures relate to a strengthening of the components of the treatment system. Under these extended measures:

- industry staff in the US would carry out a 100% inspection of picked grapes at harvest for live life stages of exotic spiders (eggs, juveniles and adults)

- all export packaging would be subject to official inspection

- fumigation procedures would be tightened to include registration of treatment facilities, registration and training of treatment operators, a higher level of documentation and record-keeping, and all treatments would be supervised by an official US inspector.

In addition all treated cartons or boxes of table grapes would require clear product identification and MAF inspectors would audit treatment facilities, both prior to exports starting and during the season.

The recommended measures include that for each consignment of grapes a sample of 920 grape bunches would be taken at random and visually inspected by a US Government inspector. The acceptance level for exotic spiders is zero live life stages. If a live life stage - including a viable egg mass - was found the entire consignment would be ineligible for export to New Zealand.

Prior to biosecurity clearance being given in New Zealand, another random sample of 920 grape bunches would undergo inspection by MAF Quarantine Officers. Again the acceptance level for live exotic spiders of all kinds would be zero and the consignment would not be accepted into New Zealand if an exotic spider was found. MAF Quarantine Service currently carry out this inspection in the USA as part of a pre-clearance programme.

Once the consignment is in New Zealand, has received biosecurity clearance, and is no longer subject to an Import Health Standard a number of contingencies have been proposed for an exotic spider detection. These range from: no action to; requiring trace back of the consignments to; recall and reshipping, destruction or further treatment.

This "programme" of measures and contingencies would be reviewed by MAF, MoH and DOC at the end of the importing season. The level of spider interceptions and post-border detections would then be assessed and any required changes to the requirements initiated at that time.


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